1. Field of the Invention
The present invention relates to a dust detector for optically detecting the quantity of dust flowing through a suction passage in a vacuum cleaner and controlling the rotational speed of the fan motor, for example, based on the detected quantity of dust.
2. Prior Art
Various dust detectors have heretofore been proposed for optically detecting the quantity- of dust flowing through suction passages in vacuum cleaners. One known typical dust detector is disclosed in U.S. Pat. No. 4,601,082.
The disclosed dust detector comprises an optical sensor including a light transmitter and a light receiver. Light is emitted by the light transmitter into the suction passage toward the light receiver. The intensity of light detected by the light receiver is varied depending on how much light is cut off or reflected by dust particles flowing through the suction passage. The quantity of dust passing through the suction passage is indirectly detected from a variation in the output signal from the light receiver. The rotational speed of the fan motor of the vacuum cleaner or a cleanliness indicator on the vacuum cleaner is controlled based on the detected amount of dust.
More specifically, if the quantity of dust particles flowing through the suction passage is large, the rotational speed of the fan motor is increased for creating greater suction power. The condition indicating a large quantity of dust flowing through the suction passage, i.e., when a surface has not yet been cleaned up, and the condition indicating a small quantity of dust flowing through the suction passage, i.e., when a surface has almost been cleaned up, are indicated respectively by differently colored lamps to allow the user of the vacuum cleaner to clean desired surfaces efficiently.
The light transmitter and the light receiver of the optical sensor are positioned such that they are exposed into the suction passage through which dust flows. During usage of the vacuum cleaner, therefore, dust particles tend to be attached to the exposed surfaces of the light transmitter and the light receiver, through which light is emitted and detected, resulting in poor performance of the optical sensor. This problem has prevented vacuum cleaners with optical dust detectors from finding practical use.